Geocentric Model

In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system), is a description of the cosmos where the Earth is at the orbital center of all celestial bodies. This model served as the predominant cosmological system in many ancient civilizations such as ancient Greece. As such, most Ancient Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circled the Earth, including the noteworthy systems of Aristotle (see Aristotelian physics) and Ptolemy.

Two commonly made observations supported the idea that the Earth was the center of the Universe. The first observation was that the stars, sun, and planets appear to revolve around the Earth each day, making the Earth the center of that system. Further, every star was on a "stellar" or "celestial" sphere, of which the earth was the center, that rotated each day, using a line through the north and south pole as an axis. The stars closest to the equator appeared to rise and fall the greatest distance, but each star circled back to its rising point each day. The second common notion supporting the geocentric model was that the Earth does not seem to move from the perspective of an Earth bound observer, and that it is solid, stable, and unmoving. In other words, it is completely at rest.

The geocentric model was usually combined with a spherical Earth by ancient Greek and medieval philosophers. It is not the same as the older flat Earth model implied in some mythology, as was the case with the biblical and postbiblical Jewish cosmology. The ancient Jewish ouranography that one can find in the Bible (Old Testament) pictured a flat Earth over which was put a dome-shaped rigid canopy, named firmament (רקיע- rāqîa').

However, the ancient Greeks believed that the motions of the planets were circular and not elliptical, a view that was not challenged in Western culture until the 17th century through the synthesis of theories by Copernicus and Kepler.

The astronomical predictions of Ptolemy's geocentric model were used to prepare astrological charts for over 1500 years. The geocentric model held sway into the early modern age, but from the late 16th century onward was gradually superseded by the heliocentric model of Copernicus, Galileo and Kepler. However, the transition between these two theories met much resistance, not only from Christian theologians, who were reluctant to reject a theory that was in agreement with Bible passages (e.g. "Sun, stand you still upon Gibeon", Joshua 10:12 - King James 2000 Bible), but also from those who saw geocentrism as an accepted consensus that could not be subverted by a new, unknown theory.